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-   -   FD with large throw? (https://www.bikeforums.net/bicycle-mechanics/487008-fd-large-throw.html)

GeorgeBaby 11-16-08 09:53 PM

FD with large throw?
 
I'm building up a Sakkit frame and I'm having a problem with the front derailleur outer limit.

Because of the way the chainstays on the Sakkit bow out, I've been forced to move the chainline out. Although the inner chainring on my triple has only about 1mm clearance from the chainstay, when I measure the distance from the middle of the downtube to the outermost chainring, it's about 55mm (compared to 50mm on two other bikes, one also with a triple).

I'm searching for FDs that can move the chain out that far. I prefer to use half-step gearing, and thus would prefer a FD compatible with that, but I'll abandon half-step if I have to. I've been trying a Shimano 600 (half-step compatible, and worked just fine with this crankset on my Surly LHT), but it can't quite make the shift up to the large chainring with the Sakkit's chainline.

What FDs can handle a large chainring difference, and can also move the chain out a long ways?

Retro Grouch 11-17-08 05:16 AM

My tandem has 160mm rear dropouts. The bottom bracket for the Ultegra triple crank has a 129mm spindle rather than the typical 118mm spindle. The distance from the CL of the seat tube to the big chainring is 60mm. It came with an ordinary Ultegra triple front derailleur which works just fine with the STI shifters.

GeorgeBaby 11-17-08 08:26 AM

Thanks. It's good to know that a standard triple will have enough throw. While I hate to abandon the idea of half-step, I'll do it if I have to.

Retro Grouch 11-17-08 05:29 PM


Originally Posted by GeorgeBaby (Post 7865063)
While I hate to abandon the idea of half-step, I'll do it if I have to.

Honestly, half step made sense when we only had 5 rear cogs and we had to stretch every combination we could out of our drive train.

With 9 or 10 rear cogs I think that half step is unnecessary. The rear cogs are generally spaced closely enough together to meet your needs.

GeorgeBaby 11-17-08 05:49 PM


Originally Posted by Retro Grouch (Post 7868498)
Honestly, half step made sense when we only had 5 rear cogs and we had to stretch every combination we could out of our drive train.

Sigh, I know -- but I had such a beautiful gearing worked out. All 5-6% differences, except at the granny end.

Panthers007 11-17-08 09:08 PM

Well you could do all a favor by publishing your recipe here. There may be others whose gearing, and such, could benefit from installing your half-step.

Hope you get the FD straightened out. I just had a war with such myself.


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